Backstop for electromagnetic devices



June 21, 1949. M. c. BECKER 2,473,351

BACKSTOP FOR ELECTROMAGNETIC DEVICES Filed Aug. 6, 1943 Fig.1. fig? 2.

i 5 l7 5 Z3 7 wi-m 9 wmvssszs; INVENTOR ATTORNEY Patented June 21 1949 UNITED STATES PATENT OFFICE BACKSTOP FOR ELECTROMAGNETIC DEVICES Maximilian 0. Becker, East Orange, N. J assignor to Westinghouse Electric Corporation,

East

7 Claims.

My invention relates to non-sticking backstops, and to a novel method of making the same, and it has particular relation to backstops for relays or other electromagnetic devices.

The need for my invention arose in connection with trouble which was experienced with sensitive, high-speed, electric relays, of a type having a pivoted beam or armature, such as have been widely used for a good many years. The particular relay which developed the trouble in question had a backstop which consisted of a bronze screw, with a rounded, polished, chrome-plated end, coming to rest against a nickel-plated brass plate. The trouble consisted in an occasional tendency of the relay to stick, in its non-operated position, with the two parts of the backstop in contact with each other. Investigation showed that, under the pressure and vibration encountered in service, the screw had a tendency to wear a tiny cup-like depression in the brass plate, which, in turn, filled with microscopic brass flakes which tended to weld or cement the two parts together.

Various efiorts to eliminate this trouble, by using a hard non-metallic substance, resulted in no entirely satisfactory solution to the problem, until a design was produced in which at least one of the members of the backstop was a hard non-metallic member having a rounded contactsurface, such as might be provided by a hard glass ball. Preferably this round-surfaced member cooperated with a flat-surfaced member of the same, or a diiierent, hard, non-metallic material, such that substantially a point contact was obtained, without a tendency to dig or wear out a cup-like depression at the point of contact.

The principal object of my invention is to provide an electromagnetic device having a movable member provided with an improved backstop of the type just mentioned.

A more specific object of my invention is to provide a hard, non-metallic ball-type element which is so mounted as to permit rotation or rolling of the ball, so as to dislodge any dust or dirt which might accumulate on top of it.

A still further object of my invention is to provide a novel type of flat-surfaced backstop member which is made by a novel method, comprising heating a hard glass ball until it has reached a plastic stage, and pressing it, with a. flat-surlaced instrument, into the open end of a thinwalled cup or" a metal having a higher coeficient of expansion than said hard glass, so that, when the device cools, the thin cylindrical wall of the cup will be under strain, so that the fiat-surfaced hard-glass contact-making member will be held tightly withtin the open end of this cup, while at the same time spreading out somewhat over the end of the cup.

with the foregoing and other objects in view, my invention consists of the apparatus, parts, details and methods hereinafter described and claimed, and illustrated in the accompanying drawing, wherein Figs. 1 and 2 are diagrammatic, slightly enlarged, side-elevational views of two relays, illustrating different forms of embodiment of backstops in accordance with my invention, Fig. 3 is a still further enlarged, cross-sectional view illustrating the method of manufacturing the fiat-topped backstop member which is shown in Fig, 2, and Fig. 4 is a similar view of the finished member which is shown in Fig. 3.

In Figs. and 2 of the drawing, I have shown a relay consisting of an electromagnet 5 and a movable armature-member which is pivoted at I, and which carries a contact-member 8. My invention relates particularly to the backstop for the movable member 6, two forms of which are shown in the drawing.

In Fig. i, I have shown a somewhat costly form of design, in which the stationary plate II has a socket I2 cut into it, with a piece of glass-tubing I3 cemented into the socket, with a slight tilt. Two glass balls is and it are inserted in the glass tube 53, with a small clearance between the balls and the inner diameter of the tube. The top ball i5 is engaged by a screw it, carried by the armature 6, and preferably having a polished sapphire contact-making plate ll spun onto its lower, or contact-making, end. The balls l4 and I5 are preferably of a hard glass.

In the operation of the device shown in Fig. 1, contact is made between the rounded surface of the hard glass ball l5 and th flat sapphire plate 11, so that substantially a point contact was made. As soon as back pressure is released, when the relay begins to operate, the top ball 15 tends to roll, thereby dislodging any dust or dirt which might accumulate on top of it, and thus preventing the sticking of the contact between itself and 3 the flat surface I! of the other part of the backstop.

In Fig. 2, a more economical design is shown, which is quite practical, and has worked out very Well in service. Instead of utilizing a movable ball Hi, I have utilized a stationary ball I9, in the design shown in Fig. 2, said ball being staked into a socket 20 which is provided in the stationary plate 2 i. It will be understood that the balls l5 and 553 are interchangeable, that is, that either the ball is or the ball !5 could be utilized in Fig. 1, and that either the ball IE or the ball l9 could be utilized in Fig. 2. Cooperating with th ball IQ is a plate-member 22 of hard glass, which is carried by the end of a metal cup-member 23 which is fastened to the bottom of a screw 26 carried by the movable armature 6.

The successful fabrication of the screw 26, carrying the flat-surfaced hard-glass member 22,

presented a considerable problem, because it was desirable to utilize a hard glass which had a melting or plastic point of such an elevated temperature as to make it undesirable as to attempt to fuse it to brass, or bronze, or similar metals, as these would also soften at this temperature. was found, by experimentation, that very successful results could be obtained if a thin-walled metal cup-member 23 were utilized, made of a metal which has a sufficiently high-melting point, but which also has a much higher coefiicient of expansion than the hard glass. A non-magnetic stainless steel was found to be a very suitable metal for this purpose.

In the process of making the flat-surfaced member 2E 22, a hard glass ball 21 was first provided, as shown in Fig. 3, having a diameter slightly larger than the inner diameter of the metal cup-member 23. A flame or flames 28 were then applied to the glass ball 21, so as to heat it, until it reached the plastic stage, at which point it was pushed into place with a polished nichrome The metal of the cup 23, having the higher coeflicient of the expansion, contracts more than the glass, when the device cools off, resulting in the thin cylindrical wall 33 of the cup being placed under strain, and tightly holding the glass endmember in place. By making the cylindrical wall 33 thin (and flexible) enough, a design is produced, in which the contraction of the metal does not exert sufiicient force to fracture the glass, thus providing a very satisfactory commercial product.

In the operation of the backstop shown in Fig. 2, and having its movable member constructed as described in connection with Figs. 3 and 4, it will be noted that a point-contact is provided between a hard glass ball 19 and a polished, flat, hard-glass surface 32, so that there is no tendency for the wearing or eroding of small depressions in the contact-surfaces, andso that,eventhoughsuch depressions should occur, the non-metallic materials will prevent the formation of microscopic metal dust which might weld or cement the two members of th backstop together. The hard glass of the members I 9 and 22 is a very desirable material to use, particularly in an electromagnetic device, because they have a hardness comparable with hardened tool-steel, without having its magnetic properties.

The relative placing of the members l9 and 22, and l 5 and I1, is such that, the rounded memher being on the bottom, any dust or dirt from the air that accumulates on them will tend to work down and away from the point of contact.

I claim as my invention:

1. A device having a movable member and a backstop for said movable member, the movable member being sensitively responsive to small forces causing it to move away from said backstop so that there will be an air-space therebetween, characterized by said backstop comprising a hard non-metallic member having a rounded contact-surface, and a cooperating hard polished member having a relatively flat contact-surface, one of said backstop-members being carried by said movable member.

2. A device having a movable member and a backstop for said movable member, the movable member being sensitively responsive to small forces causing it to move away from said backstop so that there will be an air-space therebetween, characterized by said backstop comprising two cooperating hard polished non-metallic members, one movable and the other stationary, at least one of said members having a rounded contactsuriace, one of said backstop-members being carried by said movable member.

3. A device having a movable member and a backstop for said movabl member, the movable member being sensitively responsive to small i'orces causing it to move away from said backstop so that there will be an air-space therebetween, characterized by said backstop having two parts comprising a hard glass ball, and a cooperating hard polished member having a relatively flat contact-surface, one of said backstopparts being carried by said movable member.

4. A device having a movable member and a backstop for said movable member, the movable member being sensitively responsive to small forces causing it to move away from said backstop so that there will be an air-space therebetween, characterized by said backstop having two parts comprising a rotatably mounted hard glass ball, and a cooperating hard polished member having a relatively flat contact-surface, one of said backstop-parts being carried by said movable member.

5. A device having a movable member and a backstop for said movable member, the movable member being sensitively responsive to small forces causing it to move away from said backstop so that there will be an air space therebetween, characterized by said backstop comprising two cooperating hard polished non-metallic members, one movable and the other stationary, at least one of said members being a hard glass ball, one of said backstop-members being carried by said movable member.

6. A device having a movable member and a backstop for said movable member, the movable member being sensitively responsive to small forces causing it to move away from said backstop so that there will be an air-space therebetween, characterized by said backstop comprising two cooperating hard polishednon-metallic members, one movable and the other stationary, at least one of said members being a rotatably mounted hard glass ball, one of said backstopmembers being carried by said movable member.

'7. The invention as defined in claim 1, characterized by said round-surfaced member being on the bottom.

MAXIMILIAN C. BECKER.

(References on following page) Number 6 Name Date Tupper May 18, 1926 Grossbard Nov. 8, 1927 Bruce et a1 Nov. 20, 1928 Yaxley May 21, 1929 Snyder et a1 Sept. 1, 1931 Redman Mar. 9, 1937 Ronci Aug. 2, 1938 Beggs Sept. '26, 1939 Fraenkel Oct. 29, 1940 Thorson Nov. 5, 1940 Thorson Nov. 5, 1940 Hall Dec. 31, 1940 Claesson July 20, 1943 

